The present disclosure relates to a recording medium transport device and an image forming apparatus. More specifically, the present disclosure relates to a technique for controlling the driving of transport roller pairs during transport of a recording medium.
A recording paper transport mechanism used in an apparatus such as an image forming apparatus is provided with multiple transport roller pairs that transport recording paper. A stepping motor that enables high-precision rotation control is used as a drive source for each of the transport roller pairs. In a case where the recording paper is transported by rotating the transport roller pairs by a driving force from the stepping motor, when a difference occurs between the rotational speeds of the transport roller pairs in the transport path of the recording paper, one of the following situations may result in some cases: (1) transport roller pairs pinching a single sheet of recording paper pull on the recording paper against each other; and (2) when the leading edge of the recording paper pinched by a transport roller pair that rotates at high speed goes in between the other transport roller pair that rotates at low speed, the leading edge of the recording paper is pushed into the other transport roller pair. In these situations, a greater load is exerted on the stepping motor that rotates each of the transport roller pairs, which may result in a step out of the stepping motor. A control used to prevent such step out of the stepping motor, is to increase the torque of the stepping motor when one of these situations ((1) and (2)) occurs. The following technique exists as an example of such a control. According to this technique, the number of excited phases of the stepping motor is increased/decreased in accordance with the torque required for the stepping motor, thereby rotationally driving the stepping motor while switching combinations of simultaneously excited phases.
However, the above-mentioned technique has the following problem. If the technique is used to increase torque by increasing the number of excited phases based on the load exerted on the transport roller pairs, output current increases. Consequently, the power consumption of the stepping motor increases, and also the motor temperature rises.